Cross the Bay Bridge.
Follow the signs to stay on I-580 East.
When you come to I-680, go South.
Take the Bernal Exit and go East. (to the right when you come off the ramp
At Valley Avenue make a left turn onto Valley Avenue.
Go to gate 12 (second fairgrounds entrance on the right).
Turn right at Gate 12 (into the fairgrounds).

From San Jose:

Take I-680 North
Take the Bernal Exit and go East (to the right when you come off the ramp)
At Valley Avenue make a left turn onto Valley Avenue.
Go to gate 12 (second fairgrounds entrance on the right).
Turn right at Gate 12 (into the fairgrounds).

From Walnut Creek:

Take I-680 South
Take the Bernal Exit and go East (to the right when you come off the ramp)
At Valley Avenue make a left turn onto Valley Avenue.
Go to gate 12 (second fairgrounds entrance on the right).
Turn right at Gate 12 (into the fairgrounds).

From Tracy

Take I-205 West to I-580 West
When you come to I-680, go South
Take the Bernal Exit and go East (to the right when you come off the ramp)
At Valley Avenue make a left turn onto Valley Avenue.
Go to gate 12 (second fairgrounds entrance on the right).

A map to help you in locating the the Alameda County Fairgrounds, home of the Alameda County Central Railroad Society.
Star indicates location of Gate 12.
Once you're at Gate 12:
Pull straight ahead past the golf course and the satellite betting facility.
Tell the guard at the entrance booth that you're going to the Model Railroad Club.
Proceed straight past the horse stables until you can see the 'tunnels' to the right.
Turn right and go through the tunnel.
Proceed 'straight' until you reach the end of the grass area on your right.
Turn right and find a place to park near the windmill and antique farm equipment.